AUTHOR=Anyfanti Goulielmina , Bauzá Antonio , Gentiluomo Lorenzo , Rodrigues João , Portalone Gustavo , Frontera Antonio , Rissanen Kari , Puttreddy Rakesh 

TITLE=Short X···N Halogen Bonds With Hexamethylenetetraamine as the Acceptor

JOURNAL=Frontiers in Chemistry

VOLUME=9

YEAR=2021

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2021.623595

DOI=10.3389/fchem.2021.623595

ISSN=2296-2646

ABSTRACT=<p>Hexamethylenetetramine (HMTA) and <italic>N</italic>-haloimides form two types of short (imide)X···N and X–X···N (X = Br, I) halogen bonds. Nucleophilic substitution or ligand-exchange reaction on the peripheral X of X–X···N with the chloride of <italic>N</italic>-chlorosuccinimide lead to Cl–X···N halogen-bonded complexes. The 1:1 complexation of HMTA and ICl manifests the shortest I···N halogen bond [2.272(5) Å] yet reported for an HMTA acceptor. Two halogen-bonded organic frameworks are prepared using 1:4 molar ratio of HMTA and <italic>N</italic>-bromosuccinimide, each with a distinct channel shape, one possessing oval and the other square grid. The variations in channel shapes are due to tridentate and tetradentate (imide)Br···N coordination modes of HMTA. Density Functional Theory (DFT) studies are performed to gain insights into (imide)X···N interaction strengths (ΔE<sub>int</sub>). The calculated ΔE<sub>int</sub> values for (imide)Br···N (−11.2 to −12.5 kcal/mol) are smaller than the values for (imide)I···N (−8.4 to −29.0 kcal/mol). The DFT additivity analysis of (imide)Br···N motifs demonstrates Br···N interaction strength gradually decreasing from 1:1 to 1:3 HMTA:<italic>N</italic>-bromosuccinimide complexes. Exceptionally similar charge density values ρ(r) for N–I covalent bond and I···N non-covalent bond of a (saccharin)N–I···N motif signify the covalent character for I···N halogen bonding.</p>